title: Alpha-aminoadipate delta-semialdehyde synthase mRNA knockdown reduces the lysine requirement of a mouse hepatic cell line.
abstract: Alpha-aminoadipate delta-semialdehyde synthase (AASS) is the bifunctional enzyme containing the lysine alpha-ketoglutarate reductase (LKR) and saccharopine dehydrogenase activities responsible for the first 2 steps in the irreversible catabolism of lysine. A rare disease in humans, familial hyperlysinemia, can be caused by very low LKR activity and, as expected, reduces the lysine "requirement" of the individual. This concept was applied to a murine hepatic cell line (ATCC, FL83B) utilizing RNA interference (RNAi) to achieve AASS mRNA knockdown. Cells were antibiotic selected for stable transfection of 2 plasmids that express different short hairpin RNA sequences for AASS knockdown. Compared with the wild-type cell line, AASS mRNA abundance was reduced 79.0 +/- 6.4% (P < 0.05), resulting in a 29.8 +/- 5.2% (P < 0.05) reduction in AASS protein abundance, 41.3 +/- 10.0% (P < 0.05) less LKR activity, and a reduction in lysine oxidation by 50.7 +/- 11.8%. To determine the effect of AASS knockdown on the lysine requirement, cells were grown in media containing 12.5, 25.0, 50.0, 100, or 200 micromol/L lysine. Using a segmented model approach for growth rate analysis, the lysine requirement of the cell line with AASS silencing was 43.4 +/- 1.7 micromol/L, approximately 26% lower (P < 0.05), than the lysine requirement of the wild-type cell line. These results indicate AASS knockdown decreases the lysine requirement of the cell via a reduction of lysine catabolism through the saccharopine pathway, providing the initial proof in principle that RNAi can be used to reduce the nutrient requirement of a system.
authors.affiliation: Division of Animal and Nutritional Sciences, West Virginia University, Morgantown, WV 26506, USA.
authors.forename: Beth M
authors.initials: BM
authors.lastname: Cleveland
authors.forename: Aaron S
authors.initials: AS
authors.lastname: Kiess
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Blemings
mesh_terms: D000818:Animals; D002460:Cell Line; D015971:Gene Expression Regulation, Enzymologic; D022781:Hepatocytes / Q000201:enzymology*; D008239:Lysine / Q000378:metabolism*; D051379:Mice; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012443:Saccharopine Dehydrogenases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; C533239:Aass protein, mouse; D012443:Saccharopine Dehydrogenases; D008239:Lysine